The present invention relates to cementing operations and, more particularly, in certain embodiments, to compositions and methods that include a latex and at least one of a natural pozzolan (e.g., pumicite) or cement kiln dust (“CKD”).
In cementing methods, such as well construction and remedial cementing, cement compositions are commonly utilized. Cement compositions may be used in primary cementing operations whereby pipe strings, such as casing and liners, are cemented in well bores. In performing primary cementing, a cement composition may be pumped into an annulus between a subterranean formation and the pipe string disposed in the subterranean formation. The cement composition should set in the annulus, thereby forming an annular sheath of hardened cement (e.g., a cement sheath) that supports and positions the pipe string in the well bore and bonds the exterior surface of the pipe string to the walls of the well bore. Cement compositions also may be used in remedial cementing methods, such as the placement of cement plug and squeeze cementing for sealing voids in a pipe string, cement sheath, gravel pack, formation, and the like.
Cement compositions for use in subterranean formations may include a latex to improve various properties of the compositions. For example, the latex may be included in a cement composition for fluid loss control, to provide resiliency to the set cement, and/or to reduce the issues associated with gas channeling. In general, the latex used in cement compositions is often provided as a water-in-oil emulsion containing high quantities of natural or synthetic rubber (such as styrene-butadiene rubber). However, latex-containing cement compositions typically may have reduced strength with respect to comparable cement compositions.
Cement compositions for use in subterranean formations may further include Portland cement. Portland cement generally is a major component of the cost for the cement compositions. To reduce the cost of such cement compositions, other components may be included in the cement composition in addition to, or in place of, the Portland cement. Such components may include fly ash, slag cement, shale, metakaolin, micro-fine cement, and the like. “Fly ash,” as that term is used herein, refers to the residue from the combustion of powdered or ground coal, wherein the fly ash carried by the flue gases may be recovered, for example, by electrostatic precipitation. “Slag,” as that term is used herein, refers to a granulated, blast furnace by-product formed in the production of cast iron and generally comprises the oxidized impurities found in iron ore. Slag cement generally comprises slag and a base, for example, such as sodium hydroxide, sodium bicarbonate, sodium carbonate, or lime, to produce a hydraulic composition that, when combined with water, may set to form a hardened mass.
Cement compositions may further include natural pozzolans. Natural pozzolans are generally present on the Earth's surface and set and harden in the presence of hydrated lime and water. Examples of natural pozzolans include pumicite, diatomaceous earth, volcanic ash, opaline shale, tuff, and combinations thereof.
During the manufacture of cement, a waste material commonly referred to as cement kiln dust (“CKD”) is generated. CKD, as that term is used herein, refers to a partially calcined kiln feed which is removed from the gas stream and collected, for example, in a dust collector during the manufacture of cement. Usually, large quantities of CKD are collected in the production of cement that are commonly disposed of as waste. Disposal of the waste CKD can add undesirable costs to the manufacture of the cement, as well as the environmental concerns associated with its disposal. The chemical analysis of CKD from various cement manufactures varies depending on a number of factors, including the particular kiln feed, the efficiencies of the cement production operation, and the associated dust collection systems. CKD generally may comprise a variety of oxides, such as SiO2, Al2O3, Fe2O3, CaO, MgO, SO3, Na2O, and K2O.